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Hospital CABG Volume May Not Be Best Quality Indicator

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Duke Health News 919-660-1306

CHICAGO - For coronary artery bypass graft surgery (CABG),
hospital procedural volume is only modestly associated with
outcomes and therefore may not be an adequate quality
indicator, according to a study in the Jan. 14, 2004, issue of
The Journal of the American
Medical Association
(JAMA).

There have been recent calls for using hospital procedural
volume as a quality indictor for CABG surgery, but further
research into analysis and policy implication is needed before
hospital procedural volume is accepted as a standard quality
measure, according to background information in the
article.

Eric D. Peterson, M.D., of the Duke Clinical Research
Institute
, Durham, N.C., and colleagues examined the
association between hospital CABG procedural volume and outcome
using clinical data available from the Society of Thoracic Surgeons (STS)
National Cardiac Database. The analysis included 267,089 CABG
procedures performed at 439 U.S. hospitals between Jan. 1,
2000, and Dec. 31, 2001.

The researchers found that the median (interquartile range)
annual hospital volume for isolated CABG procedures was 253
(165-417), with 82 percent of centers performing fewer than 500
procedures per year. The overall operative mortality was 2.66
percent. After adjusting for patient risk and clustering
effects, rates of operative mortality decreased with increasing
hospital CABG volume (0.07 percent for every 100 additional
CABG procedures).

"While the association between volume and outcome was
statistically significant overall, this association was not
observed in patients younger than 65 years or in those at low
operative risk and was confounded by surgeon volume. The
ability of hospital volume to discriminate those centers with
significantly better or worse mortality was limited due to the
wide variability in risk-adjusted mortality among hospitals
with similar volume. Closure of up to 100 of the lowest-volume
centers (i.e., those performing 150 or less CABG procedure!
s/year) was estimated to avert fewer than 50 of 7,110 (less
than 1 percent of total) CABG-related deaths," the researchers
write.

"Our study [expanded on] prior analyses using contemporary
analytic techniques to properly account for clinical factors,
differences in site variability, and clustering within sites.
We found that, compared with high-volume hospitals, low-volume
hospitals tended to operate on patients with higher risk and
under more emergent conditions," the author write. "Our study
further demonstrates the limitations of using hospital volume
as an indicator of the quality of CABG surgery. Hospital volume
had generally poor predictive accuracy as a means of
identifying hospitals with significantly better or worse CABG
mortality rates. Similarly, using volume as a sole referral
criterion for selecting a provider would unfairly defer cases
from nearly half of very-low-volume centers with outcomes equal
or better than overall STS mortality results."

"In this national study we found that hospital procedural
volume was only modestly associated with risk-adjusted CABG
mortality rates; however, there were many low-volume hospitals
with low mortality rates and some high-volume centers with
rates higher than expected. This study suggests that hospital
CABG surgery volume is best considered as a surrogate for
quality in a setting where other more direct process and
outcome assessments are not available. Instead it seems more
reasonable to support the continued growth of national clinical
databases, which are capable not only of tracking risk-adjusted
surgical care patterns and outcomes, but also of improving
them," the authors conclude.

The study was sponsored by the Society of Thoracic Surgeons.
Specifically, the Duke Clinical Research Institute has a
contract with the STS to be their National Cardiac Data
Warehouse and Analysis Center.

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